Ed, seriously?!? You took my fat ass up without even asking.
To answer the original, more-ambiguous question, though - It's not that hard to determine your limits without knowing exact weights. For the planes that I fly, I've made spreadsheets for W&B and run a lot of different scenarios through them so that I don't need to know exact weights in most circumstances.
For example, in the 182 I know it's pretty much impossible to load it out of CG - If I'm solo in the front, loading the baggage compartment to limits and loading the rear seat until I'm over gross still won't put it out the aft limits, and I can take a 350-pounder with me in the right seat and not be out the forward limits. Weight-wise, I can take 747 pounds in the cabin with full fuel, or 903 pounds with four hours of fuel.
In the somewhat-more-limited DA40, I also can't load it out the aft limit. I can load it out the forward limits, but if I have a person in the back seat I can't, and if I just have two in the front seats and have any doubt about whether they'll put me outside the forward limits, I know that all I need to do is throw my flight bag into the rear baggage compartment and I'll be within limits. Gross weight wise, I'm unfortunately somewhat limited in that I can only take 210 additional pounds with full fuel and be legal. In this particular case, I also know that there's some margin because there's a 110 lb. gross weight increase consisting of a collar limiting up elevator travel due to spin characteristics when heavy, so I know that if somebody lies to me about their weight or I underestimate it myself, I don't have to worry about the airplane falling apart, I've just gotta keep from stalling it until I burn a few pounds of fuel off - And I don't do stalls with pax anyway.
So - Know thy airplane. And don't be a dick.